1. Field of the Invention
The subject of the present invention is a method and a device for the regulated injection of liquid carbon dioxide (CO2L) into a liquid under pressure. The regulation of the injection of the CO2L is, according to the invention, set at a fixed flow rate, in stepped mode.
The method and device of the invention are quite particularly suitable for injecting CO2L into a liquid circulating under pressure through a pipe. The context of the present invention is that of the treatment with carbon dioxide (CO2) of any type of pressurized liquid, particularly liquids consisting of reaction mediums, industrial effluent, drinking water, etc. In the context of the said present invention, the Applicant proposes an optimized technique for the injection of liquid carbon dioxide (CO2L), this being optimized particularly both from the point of view of protection from the liquid into which the said CO2L is injected and from the point of view of environmental protection.
2. Description of the Related Art
In general, the injection of gaseous carbon dioxide (CO2G) is a technique that has been fully mastered. However, implementation of the said technique assumes prior vaporization of the carbon dioxide stored in the liquid state: 
Such prior vaporization presupposes that the user site comprises a vaporizer and entails a not insignificant power consumption. To be able to avoid such prior vaporization is obviously economically very attractive, both as regards saving on investment (absence of a vaporizer) and in terms of savings on running costs (absence of power consumption).
Thexe2x80x94directxe2x80x94injection of CO2L, while being of undisputed economical benefit, does, however, prove to be a technique which is more difficult to implement. Those skilled in the art are not unaware of this fact.
The Applicant has already proposed a technique for thexe2x80x94directxe2x80x94injection of CO2L. This technique is described in Patent Application FR-A-2,641,854. It is relatively complicated and its implementation requires substantial investment. Its implementation is in fact generally only justified in large installations if significant amounts of CO2L are to be injected. The said technique involves, for injecting a variable flow rate of CO2L (permanent and non-stepwise regulated flow of CO2L), the injection being regulated in proportional mode:
a controlled valve, of the proportional type (with variable flow rate) with no injector;
an upstream-pressure regulator for delivering the CO2L;
and is necessarily implemented with a CO2 pressure, between the said variable-flow rate valve and the said upstream-pressure regulator, which is higher than the triple point pressure of CO2 (a pressure higher than 5.2 bar).
The Applicant has wished to develop another technique for the regulated injection of CO2L into a liquid under pressure, which technique would, in particular, be easier to implement. It now proposes such an alternative technique which is particularly well-suited (but not strictly limited) to contexts in which the large investment needed to implement the technique according to FR-A-2,641,854 is not economically viable. According to the said other technique now claimed, the CO2L is injected at a fixed flow rate, in stepped mode (all or nothing). The injection is regulated, according to the invention, in a different way than in FR-A-2,641,854. It may, in absolute terms, be considered as having poorer performance.
When implementing this type of injection of CO2L the injection being regulated to occur in stepped mode, it is necessary, each time the injection of CO2L stops, to be able to avoid:
any running of the pressurized liquid treated with the said CO2L back into the device used for injecting the said CO2L (this is liable to lead to the blocking of the injector with, for example, solid residues contained in the said liquid); and
any formation of plugs of dry ice, particularly at the location of the said device for injecting the said CO2L (cold).
Faced with this technical problem which is inherent to the stepwise regulated injection of CO2L into a pressurized liquid, the Applicant recommends, each time the injection of the said CO2L stops, the intervention of a gas. The said gas has the dual function of driving back the pressurized treated liquid and of protecting (insulating) the injection device (which thus remains operational) from the said treated liquid which is liable to freeze in situ.